I agree with the rest of the guys. Try to hire somebody who is knowledgable about the subject and pay $10/hr or $10 per article. I think you may be able to get the person to write two 300-500 articles per hour, thus getting you $5 an article.
I work with general content writers on a daily basis and I feel very strongly that they don't get paid what they are worth. It is my job to find the best writers for the job and that can be very difficult to do when you have a competitive market that demands low prices. Before getting into the business I'm in now (paid posting service), I hired a guy for a rate that couldn't be beat. I foolishly bought a lot of articles upfront from him because he carried a very good reputation. I ended up editing the articles to death, just to get them sounding human. It may have saved me a bit of time because I didn't do any researching but overall it wasn't worth it. I quickly learned the lesson that you must pay more to get high quality. I also learned that you can tell when someone just recently researched the subject they are writing about and you can also tell the ones that REALLY know what they are talking about...and your readers know it too.
There's a huge difference between "general content writers" and professional freelancers. I agree with many of your points, Carjamlangley. It pays to shell out more money for quality content. With a reputable professional, you don't have to spend hours extensively editing and rewriting articles because you can count on the quality a professional writer brings to the table.